Computers and other electronic equipment are becoming more powerful and can perform a wider range of tasks. These increases in power and applicability result at least in part from an increase in the number of miniature electronic components included in each computer or other piece of electronic equipment. To help minimize the sizes of the computers and other electronic equipment and to facilitate their operation at higher speeds, electronic circuits used in computers and other electronic equipment include miniature electronic components positioned in high density packing arrangements.
One such miniature electronic component, a solid state capacitor, is a tiny rectangular “chip” that is smaller than a grain of rice. FIG. 1 shows a capacitor chip 10 that has a solid enclosed body 12 of square or rectangular cross section and made of ceramic or other dielectric material. Body 12 includes opposed upper and lower surfaces 14 and 16 spaced apart by a body thickness 18 and bound by opposed side wall surfaces 22 and 24 and opposed end wall surfaces 26 and 28. The linear region along which two edges of any of the surfaces (e.g., upper, lower, side wall, or end wall surfaces) meet and form an angle is called a corner region 32. Capacitor chip 10 includes multiple linear corner regions 32, such as, for example, (1) corner regions 32 defined by the intersection of an edge of upper surface 14 with an edge of one of side wall surfaces 22 and 24 or one of end wall surfaces 26 and 28, (2) corner regions 32 defined by the intersection of an edge of lower surface 16 with an edge of one of side wall surfaces 22 and 24 or one of end wall surfaces 26 and 28, and (3) corner regions 32 defined by the intersection of an edge of one of side wall surfaces 22 and 24 with an edge of one of end wall surfaces 26 and 28. Linear corner regions 32 may also include the point at which three edges meet, such as, for example, the point at which an edge of upper surface 14 meets with an edge of each of side wall surface 22 and end wall surface 26.
Capacitor chip 10 contains within body thickness 18 multiple spaced-apart metal plates (not shown). One terminal end of each of alternate metal plates is connected to the exterior of body 12 and is adapted by a metallizing process to form a pair of spaced-apart mutually opposed electronic contact surfaces or ends 36. One or more of contact surfaces 36 of capacitor chip 10 are striped with a solderable paste that is dried and then fired to produce surfaces that can later be soldered directly onto a circuit board. This process is commonly referred to as “termination.” U.S. Pat. No. 5,226,382 describes a machine for placing a stripe or trace of solderable paste on the contact surfaces of a chip and drying the paste so that the paste can later be fired. This machine uses a metal carrier belt or tape in which slotted rubber masks are formed. Apertures in the masks receive chips in position for processing, such as covering opposed ends of the chips with solderable paste.
A relatively new miniature electronic component, an integrated passive component (IPC) or array chip, is composed of multiple circuit components fit into a single array chip that is simultaneously solderable to one of a number of different electronic circuits. This device is called an “array chip” because it comprises a plurality or an array of circuit components, such as four or five separate capacitors stacked together in a single chip. U.S. Pat. No. 5,863,331 describes a machine for placing stripes of solderable paste on the contact surfaces of a chip array.
FIG. 2A shows a typical array chip 40 with its side wall surfaces 22 and 24 covered with stripes 42 of solderable paste. Optionally, end wall surfaces 26 and 28 may be covered with stripes 42 of solderable paste (not shown). Array chip 40 has overall dimensions such as 3.2 mm (0.125 in) long and 1.5 mm (0.060 in) wide upper and lower surfaces 14 and 16; 1.5 mm (0.060 in) wide and 0.8 mm (0.031 in) high opposed end wall surfaces 26 and 28; and 0.8 mm (0.031 in) high and 3.2 mm (0.125 in) long opposed side wall surfaces 22 and 24. Where both end wall surfaces and side wall surfaces include stripes 42 of solderable paste, formation of stripes 42 on end wall surfaces 26 and 28 may occur before or after formation of stripes 42 on side wall surfaces 22 and 24.
FIG. 2B shows that installing array chip 40 into an electronic circuit entails placing separate solderable paste stripes 42 along opposite wall surfaces, such as side wall surfaces 22 and 24 (as shown) or end wall surfaces 26 and 28 (not shown), and soldering paste stripes 42 to copper traces 44 formed on a circuit board 46. The width of each stripe 42 is typically set at 0.38±0.18 mm (0.015±0.007 in), with a 0.3±0.18 mm (0.012±0.007 in) turn-down edge at the end of each stripe 42 along the adjacent wall as shown on respective upper and lower surfaces 14 and 16 in FIG. 2A. As with other electronic components, after the paste is applied, it is subjected to a heat-drying cycle to set the paste and thereafter to a firing cycle to fuse the paste on array chip 40.
The small size of an array chip and the small differences between its width and height dimensions raise the importance of handling the array chip and its insertion into the mask of a carrier belt or tape. The multiple stripes are placed on only the appropriate circuit board surfaces, and their placement is accomplished with extreme accuracy. Splashing of the paste onto other surfaces of the array chip would provide a site for a short circuit and thereby significantly degrade electronic equipment function. Accordingly, a feed device places the array chip onto the carrier belt in a correct position and location, and the array chip is handled correctly so that the appropriate surface is exposed in proper orientation to receive the paste stripes within a specified accuracy.
Typically, miniature component carriers that transport miniature electronic components and present them for processing include an endless belt or tape that carries multiple miniature electronic components, such as capacitor chips 10 and array chips 40. The endless tape is formed with a plurality of transversely oriented, elongated apertures arranged centrally between and uniformly spaced apart along the marginal edges of the tape. Each of the apertures is adapted to receive in coplanar fixed registration a thin, resilient mask having at least one aperture, and preferably multiple apertures, of a size and shape to compliantly receive and hold the miniature components in a specific orientation so that the surfaces intended for termination extend outwardly from the mask. The term “mask” is used in the art to define an element made of silicone rubber, or other resilient material, that surrounds and partly encloses an electronic component during some stage of its fabrication process. The purpose of a mask is to provide a generally elongated, resilient-walled holder in which an electronic component may be temporarily held during the process of metallizing its opposite ends.
FIG. 3 shows an exemplary endless belt-type component carrier having a flexible metal tape 50 formed of stainless steel or other high-strength metal. Tape 50 is approximately 0.13 mm (0.005 in) thick and about 5.1 cm (2.0 in) wide and is of an “endless” variety in that it has no beginning or end but is maneuvered about a series of pulleys and sprocket wheels between various processing stations, as is described in U.S. Pat. No. 5,226,382. Tape 50 is defined by multiple spaced-apart, mutually parallel side margins 52 and 54 and includes a series of pilot or sprocket holes 56 that serve as drive perforations to receive drive stubs of drive sprocket wheels (not shown). Sprocket holes 56 are disposed adjacent to at least one and preferably both of side margins 52 and 54 and are uniformly spaced along the length of tape 50.
As shown in FIGS. 3-6, tape 50 is formed with a variety of first apertures 60 of different shape and size into which a thin, resilient mask 66 can be inserted. Each of first apertures 60 is adapted to receive in coplanar fixed registration mask 66, which includes one or more second apertures 74 and preferably a series of second apertures 74 of sizes and shapes to compliantly receive multiple electronic components in specific orientation so that their end surfaces intended for termination extend outwardly from mask 66.
First apertures 60 are preferably formed in discrete patterns and are preferably spaced centrally between and uniformly along the marginal edges of tape 50. First apertures 60 are typically a series of closely spaced round openings as shown in FIG. 3, a series of elongated rectangular openings as shown in the end portions of FIG. 4, or a series of elongated openings in repeated patterns in a side-by-side arrangement as shown in the center portion of FIG. 4. In a configuration of other than round holes, first apertures 60 are generally defined by a pair of spaced-apart, elongated side edges 62 bound by a pair of short-end edges 64. Each of first apertures 60 receives a mask 66 that is of a size and shape to remain fixed to tape 50 and to carry multiple electronic components.
Mask 66 is preferably formed of silicone rubber, but may be formed of any conventional elastomeric material having sufficient elasticity to receive and grip a miniature component in a controlled orientation. FIGS. 7A and 7B show that mask 66 is defined by a pair of spaced-apart top and bottom exterior surfaces 70 and 72 that, when mask 66 is fixed in place on tape 50, lie coplanar with and, respectively, above and below the surfaces of tape 50. In its simplest form, shown in FIG. 3, each mask 66 is cast in place about a first aperture 60 so that a plurality of masks 66 may be arranged in a pattern parallel or transverse to the longitudinal axis of tape 50. One or more second apertures 74 of a size smaller than that of first aperture 60 are formed in each mask 66 to keep the metal core of tape 50 out of contact with the electronic component. The size of second apertures 74 is slightly smaller than that of the electronic component in at least one direction so that the electronic component can be positionally accepted and resistively grasped during advancement of the electronic component from one processing stage to another. Mask 66 is defined by, in addition to respective top and bottom surfaces 70 and 72, a pair of opposed elongated slots 76 positioned intermediate of respective top and bottom surfaces 70 and 72 for receipt of elongated side edges 62 of first aperture 60 formed in tape 50. The length of removable mask 66 is less than the width of tape 50 and is preferably less than the distance between adjacent sprocket holes 56.
FIGS. 8A and 8B are, respectively, plan and enlarged fragmentary views of an alternative component carrier tape 50′ that is similar to tape 50, with the exception that silicone rubber masks 66′ molded into or coated over first apertures 60′ are of generally rectangular shape with curved ends in a core portion. Second apertures 74′ are formed in a single row in each mask 66′ along the width of carrier tape 50′.
FIGS. 7A, 7B, and 9 show masks 66 having second apertures 74 of different geometries. Mask 66 of FIG. 7A includes a series of closely spaced second apertures 74 of round shape. These second apertures 74 include a single, closed curvilinear side margin 78.
Mask 66 of FIG. 7B includes two second apertures 74 of “sawtooth” shape, each of which is capable of holding multiple electronic components. Each sawtooth-shaped second aperture 74 is an elongated aperture having multiple side margins 78 that form multiple resilient teeth 82 that extend into second aperture 74, as is more fully described in U.S. Pat. No. 5,226,382. The arrangement of side margins 78 of sawtooth-shaped second aperture 74 forms multiple individual openings 80, each of which is capable of holding a single electronic component.
Mask 66 of FIG. 9 includes multiple second apertures 74 of a “dog bone” or “bow tie” shape and including opposed side margins 88 separated along their lengths by longer distances at opposite ends 90 and by a shorter distance at a medial location 92 between ends 90. In a preferred embodiment, the slot distances become gradually smaller from opposite ends 90 to medial location 92.
An array electronic component is held in the second aperture under compression by an interference fit. For example, a 0.05 mm (0.002 in) desired interference fit nominally requires a ±0.025 mm (±0.001 in) second aperture tolerance range, and a 0.51 mm (0.02 in) thick array electronic component typically requires a 0.43-0.48 mm (0.017-0.019 in) second aperture. A less than −0.025 mm (−0.001 in) second aperture width tolerance results in a second aperture that is too tight, causing the silicone rubber nubs of the second aperture to deflect (rather than compress) and thereby cant the array electronic component held in the second aperture. A second aperture opening width of greater than 0.025 mm (0.001 in) lets the component fall out of the belt.
When loaded, individual electronic components must be centered in two directions (horizontally and vertically) within a second aperture. Currently available loading techniques require two processing steps to correctly position an electronic component within each second aperture. First, an electronic component is loaded into a second aperture such that the electronic component is centered in only one direction, typically horizontally. Second, the electronic component is centered between the top and bottom exterior surfaces of the mask. Exemplary secondary operations include, for example, (1) exposing the electronic component to a high-pressure gust of air that forces the electronic component into the desired alignment and (2) mechanically pushing the electronic component into the desired alignment, as described in U.S. Pat. Nos. 5,863,331 and 5,226,382. Both of these exemplary secondary operations involve contact with the loaded electronic component. Further, because of the tight fit of the electronic component in the second aperture, a significant amount of force is required to center the electronic component. Consequently, the secondary operation often results in mechanical damage to the loaded component. Further, the secondary operation is an additional processing step that requires the use of additional machinery and increases processing time for each electronic component.
Also, some of the prior art second aperture geometries, e.g., the sawtooth formation shown in FIG. 7B, do not consistently hold electronic components in the desired orientation, causing them to move during processing and thereby reducing the overall yield of usable electronic components. With specific reference to the sawtooth formation shown in FIG. 7B, this is so because each of the individual openings that comprise the elongated second aperture have incongruous side margins and thus lack sufficient aperture side margin grip to tightly and securely hold multiple electronic components.
Additionally, because the second apertures are shaped such that the sides of the electronic component tightly contact the side margins of the second aperture, the electrically conductive portions of the electronic components can be damaged during processing. Further, removing the terminated electronic components from the second apertures as shown in U.S. Pat. No. 5,863,331 requires a significant amount of force because of the tight fit necessary to hold the electronic component in the desired orientation during processing. This force can mechanically damage the terminated electronic component, thereby reducing the overall yield of usable electronic components. Further, during the receipt, gripping, positioning, and ejection processes, the terminated electronic component may be subject to smearing of the conductive stripes 42 as the electronic components slide along the side margins of the second aperture, which degrades the finished component's performance.
In the case of using a round second aperture 74, as shown in FIG. 7A, the side margins of the second aperture tightly contact the side and end wall surfaces of the electronic component, and any previously formed electrically conductive stripes on the electronic components can be damaged during receipt of the electronic component into the second aperture. Further, the method of removing the terminated electronic components from the second apertures described in U.S. Pat. No. 5,863,331 requires a significant amount of force because of the tight fit necessary to hold the electronic component in the desired orientation during processing. Application of this force can result in mechanical damage to the terminated electronic component, thereby reducing the overall yield of usable electronic components. Further, the terminated electronic component may be subject to smearing of the conductive stripes as they slide along the side margins of the second aperture.
What is needed, therefore, is a mask including miniature component apertures capable of receiving in a single step miniature electronic components and of gripping them in a controlled orientation during termination of the ends of the electronic components without damaging their electrically conductive portions.